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AS level Biology > Section 4 - Genetic diversity and adaptation > Flashcards

Section 4 - Genetic diversity and adaptation Flashcards

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1
Q

Define mutation

A

Any change to the quality or the base sequence of the DNA of an organism.

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2
Q

When do mutations occur?

A

During teh formation of gametes may be inherited, often producing sudden and distinct differences between individuals.

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3
Q

Define gene mutation

A

Any change to one or more nucleotide bases or a change in the sequence of the bases in DNA

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4
Q

What is substitution mutation?

A

The type of gene mutation in which a nucleotide in a DNA molecule is replaced by another nucelotide that has a different base.

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5
Q

What is the significance of substitution mutation?

A

Will depend upon the precise role of the original amino acid.

If it is important in forming bonds that determine the tertiary structure of the final protein, then the replacement amino acid may not form the same bonds.

The protein may then be a different shape and therefore not function properly.

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6
Q

How can the effect of a substitute mutation be different if the new triplet of bases still code for the same amino acid as before?

A

Due to the degenerate nature of the genetic code, in which most amino acids have more than one codon.

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7
Q

What is a deletion mutation?

A

A gene mutation by deletion arises when a nucleotide is lost from the normal DNA sequence.

The loss of a single nucleotide from the thousands in a typical gene may seem a minor change but the consequences can be considerable. The amino acid sequence will be entirely different so the polypeptide is unlikely to function correctly.

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8
Q

What is a chromosome mutation?

A

Changes in the structure or number of whole chromosomes.

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9
Q

What are the two reasons for chromosome mutations?

A
  • changes in whole sets of chromosomes
  • changes in the number of individual chromosomes.
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10
Q

How can chromosome mutations occur due to the change in whole sets of chromosomes?

A

Occur when organisms have three or more sets of chromosomes rather than the usual two.

This is called polyploidy and occurs mostly in plants.

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11
Q

What is polyploidy?

A

Occur when organisms have three or more sets of chromosomes rather than the usual two.

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12
Q

How can a chromosome mutation occur due to changes in the number of individual chromosomes?

A

Sometimes individuals homologous pairs of chromosomes fail to separate during meiosis. Known as non-disjunction a usually results in a gamete having either one more or one fewer chromosome.

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13
Q

What is a non-disjunction mutation?

A

Sometimes individuals homologous pairs of chromosomes fail to separate during meiosis. Known as non-disjunction a usually results in a gamete having either one more or one fewer chromosome.

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14
Q

What two ways does cell division occur?

A
  • Mitosis produces two daughter cells with the same number of chromosomes as the parent cell and as each other
  • Meiosis usually produces four daughter cells each with half the number of chromosomes as the parent cell.
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15
Q

What happens during sexual reproduction?

A

Two gametes fuse to give rise to new offspring.

If each gamete had a full set of chromosomes (diploid number) then the cell that they produce has double this number. - 46 in humans so each cell would have 92.

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16
Q

How are ferns different in terms of reproduction?

A

Gametes are produced by mitosis. In the fern life cycle, meiosis occurs in the formation of spores.

In more other animals meiosis occurs in the formation of gametes.

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17
Q

What is a haploid number of chromosomes?

A

During meiosis homologous pairs of chromosomes separate so that only one chromosome from each pair enters a daughter cell.

23 in humans.

When two haploid gametes fuse at fertilisation the diploid number of chromosomes is restored.

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18
Q

What is the process of meiosis?

A

Two nuclear divisions that normally occur immediately one after the other:

  1. In the First division meiosis 1 - Homologous chromosomes pair up and their chromatids wrap around each other. Equivalent portions of these chromatids may be exchanged during crossing over. By the end of this division, the homologous pairs have separated, one chromosome from each pair going into one of the two daughter cells.
  2. Second meiotic division (meiosis 2) - chromatids move apart. At the end, four cells have usually been formed. In humans, each contains 23 chromosomes.
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20
Q

In addition to halving the number of chromosomes what does meiosis produce?

A

Genetic variation among the offspring, this can lead to adaptations that improve survival chances.

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21
Q

In what two ways does meiosis being about genetic variations?

A
  1. Independent segregation of homologous chromosomes
  2. new combinations of maternal and paternal alleles by crossing over.
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22
Q

Define - gene

A

A length of DNA that codes for a polypeptide

23
Q

Define - locus

A

The position of a gene on a chromosome or DNA molecule

24
Q

Define - allele

A

One of the different forms of a particular gene.

25
Q

Define - homologous chromosomes

A

a pair of chromosomes one maternal and one paternal that have the same gene loci.

26
Q

What is the independent segregation?

A

During Meiosis 1 - when chromosomes randomly arrange themselves in pairs, one of these goes to each daughter cell.

So depending on how they line up depends on what the daughter cells chromosome combination of maternal and paternal origins looks like.

27
Q

Describe the figure

A
  1. Stage 1 -
    1. One of the pair of chromosomes includes the gene for tongue rolling and carries one allele for roller and one for non-roller.
    2. The other chromosome includes the gene for blood group and carries the allele for blood group A and the allele for blood group B.
    3. There are two possible arrangements P and Q of the two chromosomes at the start of meiosis.
    4. Both are equally possible but each produces a different outcome in terms of the characteristics that may be passed on via the gametes.
  2. Stage 2 - At the end of meiosis 1 the homologous chromosomes have segregated into two separate cells.
  3. Stage 3 - End of meiosis 2 chromosomes have segregated into chromatids producing four gametes for each arrangement. The actual gametes are different, depending on the original arrangement of the chromosomes at stage 1.
28
Q

What happens during meiosis 1 when the chromosomes line up alongside its homologous partner?

A

Crossing over

  • Chromatids of each pair become twisted around one another
  • During this process, tensions are created and portions of chromatids break off.
  • These broken portions might then rejoin with the chromatids of its homologous partner.
  • Usually, it is the equivalent portions of homologous chromosomes that are exchanged.
  • In this way, new genetic combinations of maternal and paternal alleles are produced.
29
Q

What does independent assortment cause?

A

Each number of the homologous pair of chromosomes has the same number of genes that determines the same characteristics however the alleles of these genes may differ.

Produces new genetic combinations.

30
Q

What is recombination?

A

The broken-off portions of chromatid recombine with another chromatid after crossing over.

four different cell types are produced. Increasing genetic variety.

33
Q

What is crossing over?

A

The chromatids cross over one another many times causing new genetic combinations of maternal and paternal alleles being produced.

35
Q

FORMULA

the number of possible combinations of chromosomes for each daughter cell.

A

2^n

n = the number of pairs of homologous chromosomes.

36
Q

FORMULA

variety caused by the gametes coming from different parents two different genetic complements with different alleles is combined.

A

(2^n)^2

n = the number of pairs of homologous chromosomes

Based on chromosomes staying intact throughout meiosis.

37
Q

What is selection?

A

The process by which organisms that are better adapted to their environment tend to survive and breed, while those that are less well adapted tend not to.

38
Q

What two results can be caused by selection?

A
  • Directional selection and changes to the characteristics of the population.
  • Stabilising selection - and preserves of the characteristics of a population.
39
Q

What is a polygene?

A

Characteristics that are influenced by more than one gene.

They are more influenced by the environment. Producing individuals in a population that vary about the mean.

40
Q

What types of characteristics more influence polygenes?

A

More commonly the environment than ones determined by a single gene.

The effect of the environment on polygenes produces individuals in a population that vary about the mean. When plotted you get a normal distribution curve.

41
Q

Explain directional selection

A

If an environmental change occurs the phenotypes - normally not on the mean - are best suited to the new conditions and so they are more likely to survive and reproduce. Causing the next generation to be affected.

42
Q

Explain stabilising selection

A

When an environment remains stable the individuals with phenotypes closest to the mean are favoured so are more likely to survive and reproduce passing these genes to the next generation.

Those with phenotypes on the extremes are less likely to pass on their alleles. - tends to eliminate the phenotypes at the extremes.

43
Q

What are three types of categories for adaptations?

A
  1. Anatomical
  2. Physiological
  3. Behavioural
44
Q

What two ways does cell division occur?

A
  • Mitosis produces two daughter cells with the same number of chromosomes as the parent cell and as each other
  • Meiosis usually produces four daughter cells each with half the number of chromosomes as the parent cell.
45
Q

What happens during sexual reproduction?

A

Two gametes fuse to give rise to new offspring.

If each gamete had a full set of chromosomes (diploid number) then the cell that they produce has double this number. - 46 in humans so each cell would have 92.

54
Q

What characterises a species?

A

All members share the same genes.

They differ in their combination of alleles, not their genes.

55
Q

What is genetic diversity?

A

The total number of different alleles in a population.

56
Q

What is a population?

A

Group of individuals of the same species that live in the same place and can interbreed.

57
Q

What leads to greater genetic diversity in a species?

A

The greater number of different alleles that all members of a species process.

58
Q

How can you reduce genetic diversity?

A

When a species has fewer different alleles.

59
Q

What can a greater genetic diversity mean?

A

The more likely that some individuals in a population will survive an environmental change.

As there is a wider range of alleles and therefore a wider range of characteristics.

This gives a greater probability that some individuals will possess a characteristic that suits it to the new environmental conditions.

60
Q

What does genetic diversity enable?

A

It is a factor that enables natural selections to occur.

61
Q

Now all alleles of a population are equally likely to be passed to the next generation.

Why?

A

As only certain individuals are reproductively successful and so pass on their alleles.

62
Q

What do the differences between the reproductive success of individuals affect?

A

The allele frequency in populations.

63
Q

Explain the process for the effect on allele frequency in populations.

Natural selection

A
  1. Within any population of a species there will be a gene pool containing a wide variety of alleles.
  2. Random mutations of alleles within this pool may reult in a new allele of a gene which in most cases will be harmful.
  3. In certain environments the new allele may provide an advantage over other individuals in the pop.
  4. These will be better adapted and more likely to survive in their competition with others.
  5. They are more likely to obtain the available resources and grow more rapidly and live longer/
  6. Those that reproduce successfully pass on their alleles.
  7. The new alleles that gave the parents an advantage are likely to be passed down.
  8. new individuals also have the advantageous allele, in turn, are more likely to survive and reproduce.
  9. over many generations, the number of individuals with the allele will increase at the expense of those with the less advantageous alleles.
  10. Over time the frequency of allele will increase.
64
Q

How many different species of organisms are there on earth?

A

around 1.8 million

And many more are unnamed or undiscovered. - Estimated range from 5 million to 100 million.

AS level Biology (11 decks)

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